MEXICAN BOUNDAKY LINE. 



137 



4. Gray, indurated clay, or marl, with pieces of carbonized wood ; 4 feet. 



5. Dark seam, like No. 3 ; 8 inches. 



6. Clay, like No. 4 ; 3 feet. 



7. Gray sandstone, with fragments of carbonized wood ; 2 feet. 



8. Very dark gray clay, sometimes black, and containing much organic matter in the lower 

 part, crystals of selenite, etc. ; 10 feet. 



9. Gray clay, with many fragments of carbonized wood ; harder concretions of the same clay, 

 containing carbonized wood ; 30 feet. 



10. Gray sandstone, with pieces of carbonized wood ; 2 feet. 



11. Gray clay, with thin, wedge-shaped masses of hard bituminous coal, or lignite, and 

 round lumps of sulphuret of iron. 



Slope to river-level 30 or 40 feet, in which no beds, in place, were seen. 



Many of the beds noted in the above section are seen to thin out entirely, or wholly to change 

 their character in the same bluff within a distance of not more than fifty yards ; while others, 

 so thin and obscure as to attract no attention, are seen to increase to a much greater thickness 

 in a very short space ; while about two hundred yards below where the above section was made, 

 the same line of bluif passes wholly into a soft, heavy-bedded sandstone, which breaks into 

 large, columnar masses from the top to the base of the cliff. 



The following sketch gives an example of the irregularity of the stratification in these blufis 

 of sandstone and clay : 



a. Soft, heavy -bedded, yellow sandstone, with pieces of carbonized wood. 

 5. Dark, almost black, slaty clay, with much carbonized matter. 



c. Gray sandstone, with specks of carbonized wood. 



d. Hard, reddish sandstone. 



e. Indurated gray clay, weathering to a light reddish hue. 

 /. Sandstone like the upper bed. 



These are exhibitions of isolated exposures of the sandstone, clay, etc., constituting No. 1 of 

 the Nebraska section, and which^ from its relative position to certain fossiliferous beds, under- 

 lies the calcareous strata containing Gryphcea Fitcheri, and its associated fossils. This sand- 

 stone (No. 1) will include, at least, all that portion of the Pyramid mountain on the left hand 

 side, marked in the diagram 1, while the blue clay, sandy limestone, and white, silicious lime- 

 stone, represent, as we believe, the beds Nos. 2 and 3 of Nebraska ; and this inference is 

 deduced from the facts already stated, that these calcareous beds of the Llano do elsewhere con- 

 tain the association of fossils characteristic of the horizon of Nos. 2 and 3, which we clearly 

 18 M 



